X-Ray Crystallographic and MO Studies on the Conformation of Corynoline and the Related Compounds

The crystal structure of (±)-corynoline ( 1 ) has been determined by X-ray diffraction methods. The rings B and C form the half-chair and the twist-half-chair conformations, respectively. The B/C ring conjunction exists in an anti-cis conformation, with a N …? H? O intramolecular H-bond. Conformational energy calculation by the CNDO/2 method show that the conformations of 1 , (+)-chelidonine ( 2 ), and their acetates, observed in crystal structures, are all in the one of total energy minimum.